Robby Vroemans

Synlett
DOI: 10.1055/s-0043-1763752

An efficient and practical method for the bromination of electron-rich arenes and heteroarenes was developed by using S-methyl methanethiosulfonate as the oxidant. All the bromine atoms were basically transferred to the brominated products, demonstrating the exceptional atom economy and practicality of the proposed protocol. The method reduces the amount of bromine required for this reaction system and obtains products in moderate to good yields.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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This work reports an electrocatalytic cascade method for synthesizing ketones using CO2 as a CO surrogate. By employing a synergistic combination of two earth-abundant metal catalysts, high yields are achieved in a simple setup, demonstrating the potential for sustainable and efficient carbonylation reactions.

Abstract

The construction of carbonyl compounds via carbonylation reactions using safe CO sources remains a long-standing challenge to synthetic chemists. Herein, we propose a catalyst cascade Scheme in which CO₂ is used as a CO surrogate in the carbonylation of benzyl chlorides. Our approach is based on the cooperation between two coexisting catalytic cycles: the CO₂-to-CO electroreduction cycle promoted by [Fe(TPP)Cl] (TPP=meso-tetraphenylporphyrin) and an electrochemical carbonylation cycle catalyzed by [Ni(bpy)Br₂] (2,2′-bipyridine). As a proof of concept, this protocol allows for the synthesis of symmetric ketones from good to excellent yields in an undivided cell with non-sacrificial electrodes. The reaction can be directly scaled up to gram-scale and operates effectively at a CO₂ concentration of 10 %, demonstrating its robustness. Our mechanistic studies based on cyclic voltammetry, IR spectroelectrochemistry and Density Functional Theory calculations suggest a synergistic effect between the two catalysts. The CO produced from CO₂ reduction is key in the formation of the [Ni(bpy)(CO)₂], which is proposed as the catalytic intermediate responsible for the C−C bond formation in the carbonylation steps.

Synlett
DOI: 10.1055/a-2294-4029

An efficient approach is reported for the direct halodecarboxylation of hydroxyaromatic acids by using a readily available N-halosuccinimide (halo = Cl, Br) as the sole promoter in ethanol at room temperature without any other catalyst or additive. This environmentally friendly route tolerates a wide substrate scope with good to excellent yields under convenient conditions.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Flow systems are considered as a promising solution for practical applications of light-driven reactions. Design and optimization of the reaction devices based on the characteristics of reaction types is important to achieve a full utilization of incident light and active sites of the photocatalysts, thereby achieving amplification of photocatalytic reactions.

Abstract

Photocatalytic synthesis of value-added chemicals has gained increasing attention in recent years owing to its versatility in driving many important reactions under ambient conditions. Selective hydrogenation, oxidation, coupling, and halogenation with a high conversion of the reactants have been realized using designed photocatalysts in batch reactors with small volumes at a laboratory scale; however, scaling-up remains a critical challenge due to inefficient utilization of incident light and active sites of the photocatalysts, resulting in poor catalytic performance that hinders its practical applications. Flow systems are considered one of the solutions for practical applications of light-driven reactions and have experienced great success in photolytic and homogeneous photocatalysis, yet their applications in heterogeneous photocatalysis are still under development. In this perspective, we have summarized recent progress in photolytic and photocatalytic synthetic chemistry performed in flow systems from the view of reactor design with a special focus on heterogeneous photocatalysis. The advantages and limitations of different flow systems, as well as some practical considerations of design strategies are discussed.

The review describes recent advances in homogeneously catalysed hydrogen production from biomass derived substrates, such as formic acid, alcohols, polyalcohols, sugars and cellulose. Role of bifunctional catalysts, bi-catalytic systems, catalysts immobilization, and mechanistic investigation is critically analyzed to draw a perspective from both sustainability and possible development on real application.

Abstract

Biomass–derived feedstocks for hydrogen production are crucial as an alternative to fossil fuel especially in those areas where green electricity and clean water are scarce. In this framework the transformation of simple (formic acid, alcohols) and more complex (polyalcohols, sugars and cellulose) bio–derivatives in pure hydrogen is recognized as a promising approach. Parallel to great effort in heterogeneous catalysis, milder molecular systems represent a more selective eye for alternative solutions and mechanistic insights. In the present review the introduction summarizes the challenges in the catalytic utilization of biomass–derived feedstocks, followed by the advances in homogeneously catalyzed hydrogen production from different substrates which will cover formic acid, with oustanding efficiency with noble metals and promising results with earth abundant ones and alcohols and polyalcohols, with particular emphasis to the development of heterogenized systems, ligand assisted catalysts and bi-catalytic synergistic solutions which allow to avoid base and to promote catalyst stability and recyclability. In the last part, description of hydrogen production from more complex substrates, such as sugars and cellulose, will show the role of molecular complexes in main and side reactions. Critical comments on the reported advances are provided along the whole discussion.

Synlett
DOI: 10.1055/a-2293-3243

Herein, we present a rapid and efficient method for synthesizing cyclic acetals and ketals utilizing a rotary evaporator. Unlike the conventional Dean–Stark dehydration process, which typically demands extended reaction times and copious amounts of organic solvents, our approach affords the synthesis of cyclic acetals and ketals with varying ring sizes in 30 min while using minimal quantities of dimethyl sulfoxide as the solvent. This innovative protocol features high yields, fast reactions, easy operation, and broad substrate applicability.
[...]

Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text